1. Field of the Invention
This invention relates to a switched telecommunications network, and to a method of transmitting data over such a network.
2. Related Art
Dedicated networks for the transmission of different types of data are known. For example, the public switched telephone network (PSTN) provides voice and data communications over well-established international channels. In addition, networks are becoming increasingly available which are capable of switching other types of traffic, such as computer originating data and video data. Local exchanges are provided for each of these types of data, and a user is provided with a dedicated local line, connecting the user's terminal equipment to said exchanges.
A problem with this approach is that, from the user's point of view, the bandwidth provision between the terminal equipment and the exchange equipment is significantly increased, given that bandwidth provision must be provided for each of the data services, ie voice, video and computer data. However, in existing equipment, it is necessary to provide links for each of these types of data service, given that specialised switching devices are provided for each type of traffic.
The cost of transmitting data through networks, particularly when such networks cover wide geographical areas, is largely dependent upon the level of bandwidth required by the application. Bandwidth requirements may be reduced by implementing compression algorithms. However, compression becomes extremely lossy if de-compression followed by further compression is repeated many times in order to effect transmission through the network.
It is known for private automatic branch exchanges (PABXs) to be connectable via the public switched telephone network (PSTN). Using this network, telephone handsets connectable to a PABX are connected, via the PABX, to the PSTN, thereby allowing the handsets to be operated in a manner similar to that in which stand-alone handsets are connected to the PSTN.
A problem with this approach is that many PABXs provide a far greater degree of functionality than that provided by the PSTN. Consequently, when a connection is made via the PSTN, a PABX can only function in accordance with the level of functionality provided by the PSTN, thereby significantly reducing functionality.
This problem can be overcome if a first PABX is connected to a second PABX over a dedicated link. Dedicated links of this type can be provided over any distance, thereby allowing a PABX in, for example, Australia, to be connected to a PABX in New York, while retaining much of the functionality available at each local site. However, a major disadvantage of such an approach is that the provision of dedicated bandwidth is expensive and generally prohibitive, except in exceptional circumstances.